Electrical protective system



July 17, 1928, 1,677,333

C. LE G. FORTESCUE ET AL ELECTRICAL PROTECTIVE SYSTEM Filed Sept.29, 1922 2 E 2 vl'l'l'lvl' I *1 s T 12 Q 11 12 3 15 1 E -14 mg} T 7 13 1?" Fig.5.

Separation Fig.8.

Time

WITNESSES: INVENTORS Charles LaG. Forteacue 6 Robert D. Evans. 7 BY I M C A TTORNEYY v Patented July 17, 1928.

UNITED STATES 7 1,677,333 earnu'r orn ce.

CHARLES LE G. IORTE SCUE AND ROBERT D. EVANS, OF PITTSBURGH, IENNSYLVANIA,

ASSIGNORS TO VI'ESTIIIGHOUSE ELECTRIC & MANUFACTURING COMPANY, A COR- IFOBATION OF PENNSYLVANIA.

ELECTRICAL PROTECTIVE SYSTEM.

Application filed September 29, 1922. Serial No. 591,269.

Our invention relates to electrical protective systems and it has special relation to the prevention of inductive interference in intelligence-transmission circuits, such as telephone and telegraph systems, by reason of the proximity of power-transmission sys stems.

lVhen power-transmission or railway dis tribution systems are located in proximity to telephone or other intelligence-transmission circuits, inductive interferencetends to occur in the latter circuits, with resultant impairment of service. Such undesirable effects are especially likely to occur when the transmission. line is grounded or the railway distribution system becomes short-circuitec. By reason of these abnormal conditions, relatively high induced voltages may be so impressed upon the communication circuit as to raise it to a sutficient potential above ground volta e to cause protective equipment to operate. The present types of protectors or protectivesystems, under the conditions just described, frequently operate in sueh manner as to impress a material voltage upon the telephone receiver or a repeat ing coil connectedthereto, whereby a severe vibration of the receiver diaphragm is produced, causing bad acoustic disturbance and resu ting in a bridging of the protector gaps, thereby absolutely oreventing the transmission of intelligible messages.

Que object of our invention is to provide a protective system for an intelligence-trans n ..sion circuit of. such character as to insure substantially simultaneous discharge from the respective sides of thecircuit to ground, whereby only a relatively slight acoustic disturbance is experienced in the receiver anc no interference with the transmission of messa s occurs.

. Anotner object of our invention is to provide a protective system of the character atel above. whereby the voltage imacross the terminalsof a telephone c p for example, is relatively low throughout discharge conditions of the protective means.

Viewed from another. angle, it is an object of our invention to provide a protective system of the character inv question, wherein a brush discharge to ground is in- .sured .under. excess-voltage conditions, and the formation .ofarcs or bridging. of protector ps, giving rise to severe acoustic disturbances is entirely prevented.

Another object of our invention is to provide a protective system for the purpose set forth, wherein balanced brush discharges .L lg bGi .igeneetransmission system that is located in proximity to a power-transmission sys tem, this diagram serving to illustrate one cause of acoustic disturbances in a telephone system. i

Fig.

2 is a semi-diagrammatic view of an improved protector device or gap structure that is employed in the protective system illustrated in Fig. 1, and

3 to 6, inclusive, are curve-charts graphically illustrating certain operating conditions and relations of our electrical protective system in contrast to the systems of the prior art.

Referring to Fig. 1, the power-transmis sion s cm here shown comprises a poly- Plltlfle transmission line 1, for example, which is supplied with energy from one or more suitable locations by means of. a corresponding number of al.ternating-current generators 2, each'terminus or distributing point of the line being provided with a suitable delta-star-connected transformer 3, the neutral point of the secondary transformer winding being grounded, asindicated at 4:, in accordance with a familiar practice. I The ry transformer winding supplies dis tribution conductors 5, 6 and 7 with a suitable low voltage,whereby the operationof trains or of industrial establishments may be effected. V I r The intelligence-transmission system that shown in Fig. 1 has been chosen by way of example to represent a telephone system of the usual type, although it isto. be ,understood that our invention is not so limited in its application and may be readily applied tothe protection of telegraph, signal or other systems of this character.

The illustrated telephone system con prises two operating or receiving stations'8 was, which, are. connected bythe usual and one or more ground connections, as in-' dicated at 14-.

The other illustrated station 9 is of a similar character, including a receiver 15 and a pair of protective devices 16 and 17 that are connected between the respective sides of the telephone circuit and suitable ground connections, as indicated at 18.

It will be understood that the telephone system just described is shown in a simplilied form by way of e ample only, and that all of the additional elements necessary for the usual. operation of the telephone or other intelligenes-transmission s stem have heel omitted for the sake of simplicity.

The improved form of protective device. that is referably employed in connection with our invention illustrated in Fig, 2. This device is not of our present invention, but is fully set forth and claimed in Patent No. 1,509,497 issued to Joseph Slepian, Serial No. 591,798, filed October 2,1922, for a spark gap structure, following; the broar principles laid down in a prior copcncin a application of Joseph Slepian, Patent No. 1,509.493, Serial No. 535,810, filed February 11,1922, for lightning arresters,both ofthese copending applications being assigned to the lVestinghouse Electric & Manufacturing Company. I

The structure shown in Fig. '2 comprises a pair of gaps 12 and 13 each of which is --tructed from a pair of relatively highrcslstance carbon plates or electrodes 20 and 21 of homogeneous composition, which are spaced apart a relatively short distance, such as three to iivo mils, by means of an annular spacer or ring 22 of mica. the edges which ring project beyond the edges of the carbon plates. Suitable clips or holding members 23 may be provided for the respective carbon electrodes, which are connected to one of the line conductors and to ground, respectively, as illustrated in Fig. 1.

The protective device just described, by reason of the homogeneous high-resistance material employed in its construction, prevents local heating and the concentration of the discharge, during excess-voltage conditions, at a single point, and thus produces a brush discharge between confronting sur faces. further characteristic of this type of protective device is the possibility of so constructing and arrranging' the carbon electrodes as to insure substantially simultaneous discharge of the cooperating pairs of protective devices, such as 12 and 13, as subsequently more fully described. It is be- A re lieved that the description just given, together with the operating characteristics hereinafter set forth, will provide a suflicient disclosure of the improvedprotective device for the purposes of the present specification. For a more complete exposition of the recently evolved theory of operation of this device, reference may be made to the abovenoted copending applications of Joseph Slepian.

The defects and disadvantages of the present protective systems and the method whereby the above-noted protective device overcomes such defects and disadvantages will be described first in connection with the operation of the systems shown in Fig. 1, and then by reference to the vario 2; curves that are shown in Figs. 3 to 6, inclusive. 2

it will be assumed that a fault occurs in the distribution system that is shown in Fig. l, suchas a ground at the point 19 on conductor 7. Under this condition. cur- {lows through this fault from the phase .uctor T to ground and thence to the neutral point of the secondary transformer winding, as indicated by the arrows. he current thus flowing through the earth is distributed in character, but its effect is equivalent to that of a current concentrated at a point several. thousand feet below the surface of the earth.

The conducting loop carrying the outgoing and returningcurrents is of such din'iensions as to induce a relatively high voltage in any telephone or other intelligencetransmission circuit, such as that illustrated, which runs parallel, or is located in proximity, to the power-transmission system.

By reason of the relatively great size of the earth circuit comprising: the fault 19, the voltages induced in the two sides of the telephone line circuit 10 are substantially equal. Even if the usual transposition of telephone conductors be employed, the difference in the induced voltages, under the conditions noted, negligible. Such induced voltmay be sufficiently high to cause the telephone protectors to operate.

The operating characteristics of the previously used types of protectors are graphically illustrated in Fig. 3, with ordinates representing voltages and ahscissae representing; time, under discharge conditions of the protective devices. It will be noted that the charactertistics of protective devices of the previously used types re such that, whereas one protector, such as the one corresponding to our protector 12, operates in accordance with curve A, the other protector corresponding to our protector 13, operates in accordance with an entirely dif ferent curve B.

Upon the occurrence of a high induced voltage, the potential of each protector die- Hill (ill

vice rises to avalue of approximately 350 on one side of the circuit tends toquench the are on the other side, resulting in a high voltage of oscillating character being imprlssed across the telephone receivers,

In this connection, it should be remembered that the condition for stability oi an arc is the concentration thereof at a single point. In other] wordsfit has been found practically impossible for two arcs to operate in parallel relation. For this reason, objectionable oscillation currents were set up in the telephone circuits by the breakdown of the prior typeset protective devices.

On the other hand, the characteristics of the brush discharge are entirely ditlerent. Such discharge spreads over the confronting gap surfaces (corresponding to parallel operation of the discharge) and no arcing occurs. A non-oscillatory.current is thus set up by the operation ofprotective devices of the improved type, as more fully explained later in connection with Fig. l.

In other words, protective devices of the previously used typos do not discharge uniformlyorsimultaneously, and do not possess equal discharge impedances or operate under equal. discharge voltages. In fact, a relatively high voltage, indicated by the dotted line in Fig. 6 an'iounting to 300 volts or upwards, is commonly impressed upon the telephone receivers 11 and 15.

A typical operation of the prior protective systems comprises the breakdown of the gaps 12 and 17 before thegaps 13 and 16. In this event, currentscorresponding to the above-noted potential oil 300 volts or upwards traverse these protectors and the telephone receivers 11 and 15, as indicated by the arrows. Furthcrn'iore, an arcing connition is usually set up, being caused by the initial composition and construction and subsequent disinte 'ration of the protective devices. As a result, avery severe acoustic disturbance is always experienced under the conditions described above, which is not only annoying or distressful to any person listening at the time, but is so loud as to absolutely preclude the reception of messages of any character. The resultant permanent bridging of the protector gaps frequently causes the telephone system to become inop- 'erative.

The defects of the present types of protective devices may thus be summarized as nonuniform, non-simultaneous and oscillatory breakdown of the two cooperating protective devices, by reason of the unequal dis charge voltages and impedances thereof under breakdown conditions. hloreover, the protector trequcntly becomes permanently grounded ai'ter discharging a relatively small amount of energy by reason o'lthe local heating and subsequent cmicentration of nice at a relatively few points.

On thcoiher hand; the operating Clllll'llll': teristics, under discharge conditions, of protective devices of the improved type that we employ is indicated in Fig. 1, wherein the. curve C represents the operation of protective device 12, for example, and curve D that of protective device 13. It will be noted that, by reason of the substantially uniform, simultaneous and non-oscillatory discharge of the impro ed protective devices, only a relatively small voltage, corresponding to the vertical distance between curves C and D, is impressed upon the telephone receivers 11 and 15 throughout the discharge condition of the protective means.

in other words, upon'the application of a high potential to the protector device, the voltage thcreo't rises immediately to its dis charge voltage, whereupon a brush dischargc,'but no arcing, takes place. The voltage across the protector does not rise appreciably even though relatively large currents flow through it. Consequently, the protector of the improved type cuts oil the peaks of the voltage waves, as indicated in Fig. 6.

By extended experiments, we have found that actually the amount oi acoustic disturbances received when protective devices of the improved form are employed is negligible compared with that experienced when the ilormer typCS of protective devices are employed, so that no annoyance is felt by the listener and noi terruption or confusion. ol? the in ages being transmitted occurs. in TftlCl), audibility tests indicate a reduction of acoustic disturbance by the use of the pres ent invention. in the ratio of 1500 to l. The sound loss than, the ordinary battery click.

Oscillograph records of the ope 'ation of the old and oi the improved types of devices show very clcarly'the oscillatory and nonuniform ciiaracter of currents set up by the arcing operation of the former, as contrasted with the non-oscillatory and uniform lllii currents caused by the brush-discharge operation ol? the latter. 'llhese'records also distinctly. show the great reduction in the voltage impressed upon the telephone receivers during'such discharge conditions, as coinpared with the voltage impressed thereupon during the ireakdown oil the prior protec tive devices. i i

' The iu'iportanceand value of the present invention will thus be appreciated, particularly when it is considered that, by the use of the relatively small and inexpensive protective *stem herein set forth, complicated and expensive means associated with the power-transmission circuits for preventing indtutive interference in to ephone lines, may be dispensed with.

From Fig. {t it will be noted that, instead of the local heating and arcing that occur in protective devices of the ion er type, merely a brush discharge to ground occurs when the improved form of protective de vice employed which, if the discharge current is sutiiciently large, spreads over the entire surface oi? the protector, and true arc-' ing, with its deleterious results, is absolutely prevented, as previously explained.

The method of spacing the carbon electrodes for each protector device is graphically indicated in Fig. 5, wherein the relation between discharge voltage and the distance of separation is shown. It will be noted that there is a point E corresponding to the minimum discharge voltage. In the construction of the protective device, the spacing of the electrodes in each case is so chosen that, at atmospheric pressure, the discharge voltage is practically the minimum voltage, corresponding to the point E. In other words, the inherent characteristics oi. the improved protector devices are such that they all possess a minimum discharge voltage and, consequently, under excess voltage conditions,such as are described above, the two cooperating protective devices, such as 12 and 13, will discharge simultaneously and will maintain uniform discharge conditions, as indicated by curves C and D in Fig. l.

' \Yh-ilc the curves shown herein relate particularly to the application of a high directcurrent voltage to telephone lines, the same results are obtained in the case of the application of alternating currents of relatively high value, although, as will be understood, the cont-our oi the various curves is modified by the alternating-current characteristics of the induced voltage.

The above-noted experiments indicate that the protective device shown in Fig. 2 most nearly possesses the ideal operating characteristics of simultaneous and uniform discharge under excess-voltage conditions and non-interference with the normal operation of the telephone circuits. However, it is possible that protector devices or gap structures of other types may be devised or combined to function in accordance with the principles of operation'of the present in vcntion. We, therefore, do not consider ourselves restricted to the specific form of device shown in Fig. 2, although, at present, this is the preferred form of-protector device for use in the present invention.

\Ve have thus provided a relatively simple electrical protective system possessing characteristics of substantially simultaneous, uniform and non-oscillatory discharge conditions from each side of a telephone circuit or the like to ground, whenever excess voltages are induced in a telephone line by reason of a. fault occurring in a neighboring po\ver-trauemission system. The reduction of acoustic disturbance by the use of our invention is very great and, without further expense in connection with the power-transmission liue, the transmission otmessa-ges is permitted, whereas, with the present type of protective devices, intelligible transmission is absolutely prevented and severe acoustic disturbances are experienced.

It should be urirlersteod that we do not consider ourselves limited to the particular circuit connections, structural details or arrangement of parts herein set forth, as various ii'iodilications thereof may be effected within the spirit and scope of our invention. Vi e desire, therefore, that only such limitations shall be imposed as are indicated in the appended claims.

We claim as our invention: 1. The combination with a two-conductor ohone circuit subjectto induced voltage urbanccs, of an acoustic-shock prevent- 5 comprising two similar autovalve d between each conductorrand ground, eacn of said autovalve arresters being characterised by having two high-resistance plates spaced by a gap of the order ol 3 mils in air, the resistivity of said plates being sutliciently high to prevent concentration of the brush discharge into an arc during ordinarily expectable induced-voltage disturbances.

2. The con'ibination with a two-conductor telephone circuit subject to induced voltage disturbances, of an acoustic-shock preventing means comprising apparatus providing two similar discharge gaps of a valve type characterized by operating substantially as an open circuit for voltages below the breakdown voltage and operating, after brealc down, at a voltage of the same order of magnitude as the breakdown voltage throughout the duration of the discharge, whereby sud den drops in voltage during the discharge are avoidet, connections of substantially negligible impedance being provided for introducing one of said gaps between each conductor and ground.

In testimony whereof, we have hereunto subscribed our names this 28th day of Sep tember, 1922. p

CHARLES LE Gr. FORTESCUE. ROBERT D. EVANS.

one of said arresters being con- 

